Less perhaps has been done in the way of actual definite scientific experiments upon mental actions and processes than in almost any other department of science, and this is partly accounted for by the fact that the other sciences require to be largely advanced before we can use them to examine mental action,
and partly also because (as occasionally happens) the latter has been a neglected subject of research. During the past few years however, various experimental investigations have been made, especially by Donders in Holland, and Mosso in Turin, for the purpose of elucidating the physical conditions of mental action; and it has been found that instead of an act of thought being instantaneous, as was formerly believed, it requires a variable time.[[13]] Numerous desultory experiments made upon dreamers, and with drugs, alcohol, &c., upon persons in the waking state, also prove that mental phenomena are amenable to scientific research. F. Galton has even proposed experiments and methods for measuring the mental faculties of different persons.[[14]] The effects of exciting different parts of the brain of animals by means of electric currents, and the localization of the functions of the brain effected by the experiments of Ferrier, Hirtzig and others, also tend to throw further light upon mental phenomena. The fact alone that mental actions and conditions may be made the subject of experiment, and consequently of observation, comparison, analysis and inference, proves that they may be rendered sources of new facts and principles, and are therefore within the domain of science. As the dependence of mental phenomena upon physical conditions has been clearly demonstrated, an extensive reduction of them to scientific laws is only a question of time and labour.
The principles of nature and the modes of mental action are the same for all men. It necessarily follows from the essential nature of truth and the invariability of the chief methods of detecting it, that the criteria of truth in mental science, and the mental powers and processes by which truth is arrived at and detected in that science, are essentially the same as in the physiological, chemical, and physical ones. In each of these subjects, we first, either with or without the aid of experiment, make observations, record facts, compare them, and draw conclusions from our comparisons; we also group the facts, and the conclusions, in every possible way, and then draw other conclusions; we also analyse, combine, and permutate the various truths arrived at, and cross examine the evidence in every possible manner in order to extract from it the greatest amount of new knowledge. And in each case we employ as the criteria of truth, the test of consistency with the whole of the evidence bearing upon the case, and especially with the great principles of science. We determine what is true, chiefly by comparison with those principles, because they are the most firmly established true ones and the most universal. There is no royal road to truth, and no special mental faculty for detecting it in any subject; and it is in consequence of our mental faculties being so very finite that we have no easier way of arriving at truth.
No dogmatic teaching can ever, except by accident, fully explain to man the true nature of mind; and
only in proportion as man becomes enlightened by extension of new scientific knowledge, especially in physiology, will he be able to view himself in a true aspect apart from his consciousness. Science penetrates deeper than metaphysical speculation, into the nature of mental action, chiefly because metaphysics deals only with old ideas, whilst science furnishes us with new experience and therefore with new conceptions and wider evidence.
Fallacies are very prevalent, every subject of human study is liable to a very large class of errors arising from the extremely imperfect state of our knowledge, and in very few subjects is our ignorance as great as in that of mental and moral phenomena. Every different subject of study also, has, in consequence of its special peculiarities, its own peculiar class of fallacies, into which the student of it is likely to be led, unless he is previously guarded against them. In accordance with this truth, the study of man's nature, especially the mental and moral portions, is particularly liable to a class of errors arising from the circumstance, that the phenomena to be observed and the observing power are intimately connected together, each influencing and disturbing the other. The obstacles to our arriving at truth in the study of mental and moral actions, are greater and more frequent, the more nearly and intimately related the phenomena to be observed and contemplated, are to the observing and contemplating faculty, or rather to the contemplative action. When the two mental
actions are extremely intimate, as when attention is directed to the action of will (which is itself a conscious act of attention) undisturbed thought becomes very difficult; and when further, the contemplative faculty attempts to contemplate itself, as when consciousness attempts to observe consciousness, in order to define it, the attempt results in almost complete failure, probably because the two actions (observing and being observed) being opposite in kind, cannot coexist at the same time in the same structure. Knowledge of the exact nature of consciousness therefore, will probably only be arrived at by indirect means, when physiological and other knowledge is sufficiently advanced.
Consciousness, when uncorrected by sufficient knowledge and inference, is a great source of error. That which we feel, we think exists whether it does or not, until the subject is correctly explained to us. The incessant and irresistible obtrusion of consciousness exercises dominion over every mind, even of our greatest thinkers, and causes disturbance and interruption in nearly every train of thought. It is largely the cause of some of our most general ideas and emotions and insensibly influences our views of man and nature. It produces true impressions as well as erroneous ones. It is a cause of the feeling that an occult spirit exists within us independent of our material structure. Combined with the almost equally persistent impression of the uniformity of nature, it largely produces the idea that the spirit within us,
will live and be active for ever. And by uniting with the frequent impressions of failure of our efforts and desire for more perfect enjoyment, it largely originates the idea of everlasting happiness.